Embryology

Question 1

NF-1: 3-5 cm flat, pigmented spots on trunk and multiple, soft, fleshy, cutaneous tumors on trunk and neck (cafe au lait spots) arising from AD mutations in NF-1 gene arising soon after birth and are at increased risk of optic gliomas, pilcoytic astrocytomas- Pt awakening at night

Cutaneous neurofibromas arise during early adolescense (benigh nerve sheath neoplasms) and increase with age- these are comprised of Schwann cells (neural crest)

Answer 1

Optic glioma

Question 2

During the first sex weeks of gestation the embryo has gonad,s a paramesopnephric duct and a mesonephric (wollfian) duct.

Differentaiton of the repro system occurs in the follow sequence:

Answer 2

1) Gonadal stage: primordial germ cells originate near the yolk sac and move towards the gential ridge, forming primitive gonads consisting of germ cells, supporting cells and steroiogenic cells. Uner the influence of SRY, male gonads begin to secrete testosterone from Leydog ells and mullerian-inhibiting factor from Sertoli cells
2) Ductal stage- development of either the paramesonephric or mesonephric ducts
3) Genital stage- The genital tubercle gives rise to the gland penis in males and the glans clitoris is girls. The urogenital forms trnaform into the ventral aspect of the penis in male and labia minora in females. The genital swellings becomes the scotum and labia majora. The urogenital sinus becomes the bladder, urethra, prostate, and bulbourethral glands in males and the lower vagina, bladder, urethra, and Bartholin glands in girls

Question 3

During early embryo, the lumen of the midgut is connected to the yok sac cavity via the vitelline duct, which obliterates during the 7th week. Partial failure to obliterate leads to a Meckel’s diverticulum

may present as rectal bleeding or obstruction, however most cases are asymptomatic

In contrast to false diverticula, these consist of all three parts of the intestinal wall: mucosa, submucosa, and muscularis

Answer 3

Rule of 2’s with Meckels:

2 inches in length

2 ft from ileocecal valve

2% are symptomatic

males 2x likely to be affected

Question 4

Fetal circulation- oxygenated blood rom placenta is devliered to the fetus via the umbilical vein. Thus the umbilical vein has the highest oxygen content in fetal circulation. Blood from the umbilical vein is first delivered to the liver, where it bypasses the hepatic circulation via the ductus venosus and enters the IVC.

From the IVC, blood is delivered to the heart where it is either pumped into the pulmonary circulation or directly into the left heart via the foramen ovale.

Answer 4

A fraction of pulmonary blood enters the dctus arteriosus directly into the descending aorta

From the aorta, blood circulates to all of the fetal tissues

Deoxygenated blood is then delivered from the fetus back to the placenta via the paired umbilical arteries

Question 5

The spleen is derived from mesoderm of the dorsal mesentery but receives blood supply from the foregut derivative splenic artery off the celiac trunk